ceph: make gitbuilder host configurable
ceph: make gitbuilder host configurable

Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@inktank.com>

SUSE/teuthology,robbat2/teuthology,ktdreyer/teuthology,dreamhost/teuthology,caibo2014/teuthology,michaelsevilla/teuthology,caibo2014/teuthology,yghannam/teuthology,SUSE/teuthology,ktdreyer/teuthology,dmick/teuthology,ivotron/teuthology,dmick/teuthology,ceph/teuthology,SUSE/teuthology,dreamhost/teuthology,dmick/teuthology,tchaikov/teuthology,ceph/teuthology,zhouyuan/teuthology,michaelsevilla/teuthology,yghannam/teuthology,t-miyamae/teuthology,ivotron/teuthology,t-miyamae/teuthology,zhouyuan/teuthology,tchaikov/teuthology,robbat2/teuthology